1. Field of the Invention
The present invention relates to a method of and apparatus for manufacturing semiconductor devices. More particularly, the present invention relates to a method of and apparatus for forming a film on a plurality of wafers.
2. Description of the Related Art
Generally, semiconductor devices are manufactured by repeatedly performing a series of processes, such as photolithography, etching, ion implantation, chemical and mechanical polishing and the like, on a wafer. The respective conditions under which these processes are performed must be optimized such that the semiconductor devices manufactured by the unit processes have enhanced functions and a minimal rate of failure. In addition, the time periods under which the respective processes are carried out should be optimized so as to enhance the productivity of the overall semiconductor device manufacturing process.
The respective unit processes have been gradually improved in consideration of these goals. However, productivity still lags in many areas of the manufacturing process and the respective unit processes are still prone to failures having a certain root cause.
For instance, the respective unit processes for manufacturing the semiconductor devices includes a batch type chemical vapor deposition process used to form respective films on a plurality of wafers at the same time. The batch type chemical vapor deposition process is carried out in a furnace maintained at a high temperature. Thus, a native oxide is frequently formed by the reaction of silicon at the upper surface of the wafer and oxygen. In other words, an undesired native oxide is grown on the surface of the wafer before the actual CVD process begins. Accordingly, a film is formed on the native oxide and not on the surface of the wafer, whereby a process failure will occur.
FIG. 1 is a sectional view of a semiconductor device in which a native oxide has been formed on the surface of the wafer. As shown in the figure, an oxide film 12 is formed on a silicon substrate 10. A contact hole is then formed to expose a portion of the silicon substrate 10 in which a source or drain is formed, for example. Subsequently, a conductive film 16 is formed by chemical vapor deposition on the oxide film 12 to fill the contact hole and contact the exposed portion of the substrate 10.
However, as mentioned above, before the conductive film 16 can be formed, a native oxide 14 having a thickness of a few Å to a few hundred Å is formed on the surface exposed by the contact hole. This native oxide 14 is an insulating material formed between the underlying silicon substrate 10 and the conductive film 16. Accordingly, contact resistance increases. This increase in the contact resistance results in a corresponding decrease in the operation speed of the semiconductor device and otherwise degrades the electrical properties and reliability of the device.
Accordingly, the native oxide and organic foreign particles are removed prior to the chemical vapor deposition process. This removal of native oxide and organic foreign particles is generally carried out by a wet etch process in which the wafers are dipped in an etch solution in a separate wet etch apparatus. In other words, the native oxide is removed from surfaces of the wafers using chemicals, the chemicals are cleaned from the surfaces of the wafers, and the wafers are dried. Afterwards, the wafers are transferred into the furnace whereupon the chemical vapor deposition process is performed.
In the method described above, even after the native oxide is removed, the silicon component of the wafer surface may again react with oxygen such that a new native oxide is grown on the surface of the wafer. To prevent this from occurring, the deposition process must be performed within a certain time after the native oxide has been first removed from the surface of the wafer. Otherwise, the new native oxide must be removed from the surface of the wafer.
However, the mass production of semiconductor devices makes it very difficult to perform the deposition process directly after the wet etch process. Also, incorporating the wet etch process into the overall manufacturing process reduces the manufacturing rate because the wet etch process equipment and the deposition process equipment are separately operated.
Moreover, a native oxide cannot be completely prevented from re-growing on the surface of the wafer even when the deposition process is performed within the time period called for, by the process recipe, after the native oxide is removed. A native oxide grows rapidly on the surface of the wafer while the wafer is loaded into the furnace because the reaction between oxygen and silicon occurs more actively occurs at the high temperature maintained in the furnace. Thus, it is very difficult to use wet etching to prevent a native oxide from residing on the surface of the wafer before the CVD process is initiated.
Japanese Patent Laid Open Publication No. 4-188722 discloses a heat treatment apparatus aimed at removing the native oxide from a surface of a wafer and preventing the native oxide from re-growing on the surface. The heat treatment apparatus includes a furnace in which a film is deposited on a wafer, a dry etching chamber disposed to one side of the furnace, a loadlock chamber connecting the dry etch apparatus to the furnace, and a robot arm for loading or unloading the wafer into and from the furnace. In this apparatus, the deposition process is carried out after the native oxide is removed by dry etching and the wafer is loaded into the furnace via the loadlock chamber.
However, this process requires a great deal of time because the apparatus uses a robot arm to transfer the wafers from the loadlock chamber. More specifically, the wafers are transferred by the robot arm into a boat in the dry etching chamber. The robot arm can transfer only a few sheets (approximately five sheets) of wafers at a time. Thus, the transfer operation must be performed a numbers of times to transfer the total number of sheets of wafers (25 sheets to one hundred sheets) of one batch. Once the dry etching is completed, the wafers disposed in the boat within the etching chamber are again transferred, this time to a boat within the furnace. After the deposition process is completed, the wafers are unloaded from a boat within the furnace and are transferred out of the furnace using the robot arm.